Abstract

Aryl hydrocarbon hydroxylase was induced in the absence of mitogens by several compounds in a stable, human B-lymphocyte cell line (RPMI-1788). Over the dose ranges tested and on molar basis the inducers, in decreasing order of potency, were 2,3,7,8-tetrachlorodibenzo-p-dioxin, dibenz(a,h)-anthracene, 3-methylcholanthrene, benzo(a)pyrene, and 1,2-benzanthracene. Potential inducers which, paradoxically, diminished basal aryl hydrocarbon hydroxylase, included 7,12-dimethylbenzanthracene, 2,5-diphenyloxazole, and chrysene. Induction under optimal culture conditions ensured maximal activities 3- to 4 fold above basal aryl hydrocarbon hydroxylase. The characteristics of the induced [dibenz(a,h)anthracene] and basal enzymes were found virtually identical. Both had similar pH curves (optima at 8.25) and inhibitor specificity (α- and β-naphthoflavones, metyrapone, and 2-diethylaminoethyl-2,2-diphenylvalerate in decreasing potency). Induced and basal enzymes exhibited similar half-lives (41, 46 hr), apparent activation energies (16.7, 16.6 kcal/mol), temperature optima (37–38, 38–39°), temperature-dependence of denaturation (range, 42–50°), and apparent Km's with benzo(a)pyrene (1.8, 0.8 µm). The small difference in the apparent Km was related to enzyme concentration in the incubation rather than to the quality of the enzyme.

Footnotes

↵1 Supported by Grants CA-13038, CA-17538, CA-05928, and CA-14413 from the National Cancer Institute and Grant CTR-1253 from the Council for Tobacco Research.